1. Field of the Invention
The present invention relates to a method of cooperative transmission in an SISO (single input single output) OFDMA (orthogonal frequency division multiple access) uplink system. More particularly, the present invention relates a method of cooperative transmission technique using STBC. We can overcome limitations of MIMO (multiple input multiple output) and give the gain of cooperative transmission diversity in a concept of virtual MIMO with single transmit antenna
2. Description of the Related Art
Orthogonal frequency-division multiple access (OFDMA) is a combination of orthogonal frequency-division multiplexing (OFDM) and frequency division multiple access (FDMA). Recently, the OFDMA was proposed as one of the reasonable solutions for broadband wireless multiple access systems such as the digital video broadcasting—return channel terrestrial (DVB-RCT) system which is return channel in terrestrial digital video broadcasting (DVB-T). For improved performance of DVB-RCT system, space-time block code (STBC) which increases the capacity and reliability could be considered, and MRC which provides best performance with highest average output SNR could be applied.
In OFDMA uplink system with two transmit antenna, a STBC is exploited to efficiently detect the information by subscriber terminal. To apply a transmitting diversity (TD) scheme, the full rate space-time block code proposed by Alamouti is used at the base station as
                    x        =                  [                                                                      x                  1                  p                                                                              x                  2                  p                                                                                                      -                                                            (                                              x                        1                        p                                            )                                        *                                                                                                                    (                                          x                      1                      p                                        )                                    *                                                              ]                                    [                  Equation          ⁢                                          ⁢          1                ]            
where each row is transmitted from a certain antenna at the same time, and each column is transmitted from a same antenna within two time slot and (·)* denotes the complex conjugation operation.
And the signals via two antennas are combined with MRC technique as a kind of receiving diversity (RD). Under the assumption of perfect channel estimation, the combined signal of p-th user, in the frequency domain, is represented by{circumflex over (X)}p=(H1p)*·R1p+(H2p)*·R2p  [Equation 2]
where {circumflex over (X)}p and H1p denote detected signal and the channel between the transmitter and the i-th receiver respectively. And R1p represents the received signal of p-th user at i-th antenna in [Equation 2].